In 5-axis CNC machining, it is important to avoid drastic changes of tool orientations for improving kinematics performances of two rotary axes of 5-axis machine tools and achieving good machining surface quality. For this purpose, in this paper, a minimum-acceleration local modification (MALM) method is proposed to plan the tool orientations for 5-axis ball-end machining. First, with several specified representative tool orientations (RTOs), initial tool orientations are generated efficiently along the tool path by quaternion interpolation (QI) method while guaranteeing no machining interferences. Then, the generated tool orientations are checked whether the angular accelerations of the rotary axes exceed their drive limits, and the over-limit areas (OLAs), which are involved in tool orientation modification, are subsequently identified. In the OLAs, the minimum-acceleration model for local modification of tool orientations is given in machine coordinate system (MCS), and then is used to adjust the tool orientations to improve the kinematics performance of the rotary axes. Finally, the experiments demonstrated that this method can improve significantly the kinematics performances of the rotary axes. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.